The purpose of this research is to develop methods for the production of a safe and effective vaccine against retroviruses. The ultimate goal is to apply these studies toward protection from the human retroviruses associated with cases of adult T-cell leukemia and acquired immune deficiency syndrome (AIDS). We have chosen the Feline leukemia viruses as a model system. Although the genomic structure of FeLV differs from the human retroviruses, its mode of infections and replication is similar. Also, certain isolates of FeLV induce an immune deficiency (Feline AIDS or FAIDS) not unlike the disease associated with HTLV III/LAV. We will use synthetic peptides to generate subunit vaccines. We have pinpointed three areas of the envelope gene for more intensive study based on preliminary results. We will synthesize additional peptides from these regions in order to maximize the neutralizing response obtainable by use of synthetic peptides as immunogens. Monoclonal antibodies will be prepared to synthetic peptides which induce a neutralizing response. These antibodies will be used to determine epitopes of these peptides which are critical for neutralization and additionally, will be compared to neutralizing monoclonal antibodies made against intact virions. We will compare the relative neutralizing titers as well as perform competition experiments for native antigen which will give us a measure of the relative affinity of monoclonal antibodies generated against synthetic peptide antigens to those made against the viral antigens. We will thus be able to predict peptide structures which best mimic the native antigen. We will test the relative susceptibilities to neutralization of six molecularly cloned FeLV isolates, comprising multiple members of the FeLV subtypes. Nucleotide sequence analyses will be performed on cirtical regions of the envelope gene of resistant virus isolates to determine if sequence variations are responsible for this resistance to neutralization. Where required, additional peptides corresponding to such sequence changes will be synthesized and tested. We will also explore the role of carbohydrate on the host's response to the envelope glycoprotein. We will immunize cats with untreated and deglycosylated FeLV and compare the relative neutralizing titers. Collaborative studies will also be performed to test the effects of deglycosylation on the immune response to the gp120 envelope protein of HTLV-III. These studies should yield an accurate assessment of the practicality of synthetic vaccines against a family of retroviruses. Furthermore, the proposed studies will make significant contributions to our understanding of retrovirus structure and factors influencing the host's perception of the invading virus.